The essential things to know about the Protestant Reformation would include the following:

It began in Germany in the early sixteenth century with a public critique of the Catholic Church by Martin Luther.

Luther's movement spread largely with the assistance and support of powerful German princes.

The Reformation essentially involved an emphasis on receiving grace by faith alone, rather than through the sacraments and other Church rituals.

Other major movements occurred in Zurich (Huldrych Zwingli) and, more importantly, in Geneva (John Calvin.) Calvinism would be very influential in Britain, Holland, France (for a short time) and eventually New England.

The Reformation led to religious and political conflict that included civil war in France, separation of the Church of England from Rome, and the Thirty Years' War.